Field of the Invention
The present invention relates to engine management and acquisition of data synchronously with the revolution of the engine crankshaft. The invention more particularly concerns the field of angular prediction methods enabling determination of the precise geometrical position of the crankshaft.
The invention may find applications in the research laboratories of engine manufacturers to assisting in the design of motor vehicle engine management systems. It may also be integrated into the engine management systems in a volume production vehicle
Description of the Prior Art
During the operating cycle of an internal combustion engine numerous actions must be synchronized to the geometrical position of the crankshaft. This applies to control of the injection of fuel, control of the spark plugs and management of the distribution units. Actuators such as fuel injectors and ignition coils must be controlled according to particular angular positions of the engine cycle.
The increasingly frequently adopted industrial use on volume production vehicles of processing algorithms for optimizing engine performance necessitates the acquisition of signals over precise angular windows as well as measuring the instantaneous speed of the engine. For example, it is necessary to know the angular position of the crankshaft and its instantaneous speed in the context of control systems enabling optimization of the operating point of an internal combustion engine by the processing in real time of meaningful parameters of its operation, such as the pressure in the various combustion chambers at a series of successive moments of each combustion cycle.
To perform these various actions, an engine is equipped with a computer that requires precise information of the position of the crankshaft. To satisfy these requirements, the crankshaft is equipped with a toothed wheel and with a sensor that detects the passage of the teeth with the objective of informing the processor responsible for controlling the control and/or command units of this. This toothed wheel is referred to as an “engine target”.
The latter is a disk generally placed at the level of the engine flywheel. Teeth are machined on the periphery of this disk in a regular manner. To provide turn synchronization, it is common to create a space by eliminating one or more teeth. The teeth are referred to as “missing teeth”. A target very often encountered in Europe has 58 teeth on its periphery. This in fact means regular machining of 60 teeth, each having a width of 6° V, and a space defined by the absence of two teeth. This topology is commonly referred to as 58X, or even 60-2.
To generalize, it may be considered that a crankshaft target may include a plurality of openings at its periphery. The interval between each opening is referred to as a sector. Each sector has a series of regular teeth followed by an opening of n teeth in width. The target may be expressed in the form: p*(m−n) with                p being the number of sectors per engine turn where the geometry (m−n) is defined        m being the number of regular teeth that the sector would include with no opening        n being the number of missing teeth on the sector (size of the opening)        
To return to the 58X target example, it is defined in the form “1*(60-2)”.
However, to make use of an engine target, it must be possible to position a tooth numbered 1 with a perfectly known position, that is to say it must be possible, on the basis of the signal from the sensor, to determine the precise moment at which a particular tooth (tooth 1) passes in front of the sensor. The detection of the opening characterized, as described hereinabove, by the absence of one or more teeth enables an absolute reference to be obtained, thus indicating the precise position of the crankshaft. By definition, the tooth 1 may be set as that which follows the two missing teeth.
Engine targets are associated with a sensor which detects the passage of the teeth. The signal delivered by the sensor is an analog signal in the case of a variable-reluctance sensor and must be conditioned so that it can be used. The result of this conditioning is a signal (CS) in which a rising or falling edge reflects the middle of a tooth. In the case of a Hall-effect type sensor, the digital signal delivered may be used directly. It is precisely on the detection of this rising or falling edge that the processors base their synchronization of the operation of the engine.
Complementing information coming from an instrumented sensor on the crankshaft (AAC), the exact knowledge of the geometrical position of the crankshaft enables precise positioning over an engine cycle of the injection and/or ignition windows for each of the cylinders.
However, controlling the actuators of internal combustion engines necessitates an angular resolution of the order of 0.1°, and thus much higher than that obtained with the raw signal (CS) delivered by the crankshaft sensor (6° for a target of 1*(60-2) type).
To obtain high-resolution information as to the angular position of the crankshaft target, it is known to apply interpolation to the raw signal (CS) to increase the angular resolution.
The method employed uses a digital phase-locked loop (PLL) with an operating period programmed to be equal to the period of the tooth fraction to be generated. The latter is obtained by division of the period of a tooth that it is required to interpolate by the number of tooth fractions that it is required to generate. It is necessary to effect a fractional division and to manage the fractional parts through successive accumulation so as not to lose precision.
There is also known a method of determining the instantaneous angular position of a crankshaft target avoiding these problems, as for example the method described in French patent application No 13/61854. In this method, the angular resolution of the signal is increased by interpolation and a high-resolution signal is generated representing the passage of tooth fractions in front of the sensor as a function of time.
FIG. 1 shows the various phases of synchronization of such a system.                A) Tooth synchronization phase during which, three consecutive periods (teeth) are typically measured to be certain of not being on an opening        B) Sector synchronization phase during which, detection of the opening is made        C) Cycle synchronization phase during which detection of a known profile on the camshaft target is made        D) System synchronized        
As this figure shows, the total duration of the synchronization phase depends on the number of crankshaft target sectors, the number of profiles that can be identified on the camshaft target and the stopped condition of the engine which is determined by the number of teeth between the stopped position and the first singularity of the crankshaft target. For a 58X target and a single crankshaft target, this can represent up to two engine revolutions.
The measurement of the period of the crankshaft teeth is the main information source of such a system. During the phase of stopping the engine, as the engine rpm decreases, the tooth period increases until it exceeds the measurement capabilities of the system, leading to desynchronization of the system and making complete synchronization obligatory each time the engine is started.